As the battery charge depletes during use of a battery-powered device, the corresponding battery voltage decreases. At some point, the battery voltage becomes unacceptably low as the battery is discharged such that the device powers down. For example, it is conventional for a handset to power down if the battery voltage drops below a software cutoff threshold voltage such as 3.5 V. The device is then unusable until the battery is recharged. Because consumers demand extended use times, it is desirable to delay the device shutdown as long as possible.
Within a mobile device, the battery may power numerous different power rails that supply corresponding power domains. Each power rail is sourced by a corresponding power regulator such as a low dropout regulator. The devices typically include a power management integrated circuit (PMIC) to manage the power regulators for the various power rails. To extend battery life, it is conventional for the PMIC to power down assorted ones of the power rails while the device is in a standby or sleep mode. For example, when not in use, a mobile telephone is predominately in an idle standby (sleep) mode. The mobile telephone will then wake up periodically according to its discontinuous receive (DRX) cycle to cheek for messages or calls. When in sleep mode, unnecessary power rails are typically powered down to extend battery life. If a power rail is instead sourced during the sleep mode, transistors and other devices coupled to the power rail will conduct leakage current that unnecessarily discharges the battery.
Although modern power management techniques increase operating times, there is a need in the art for additional battery life.